1. Field of the Invention
The invention relates generally to spread spectrum mobile communication networks, and more particularly, to a method and apparatus for estimating cell interference in a spread spectrum mobile cellular communication network.
2. Description of Related Art
In spread spectrum mobile cellular communication networks, the signal power level between base stations and mobile units is carefully controlled. For example in code division multiple access (“CDMA”) mobile communication system versions, a mobile unit calculates the channel quality of a signal transmitted from the base station and periodically reports this measured channel quality to the base station. The base station may then adjust the gain of future transmissions to the reporting mobile unit accordingly. In addition, the mobile unit may determine and report the channel quality of pilot signals received from other base stations. Depending on the reported channel quality of other pilot signals, communication between the mobile unit and another base station may be established.
In CDMA IS2000 standards prior to release C (1xEVDV), the channel quality for a pilot signal of a nearby base station is defined as the ratio of the pilot signal energy to the total noise and interference power as experienced by the mobile unit. In the CDMA IS2000 standard release C (1xEVDV), the channel quality (“C/I”) of a pilot signal of a nearby base station is defined as the ratio of the pilot power to the interference density (Nt), where Nt is the noise level experienced by the mobile unit when the received signal is despread using a target cell P/N sequence, excluding all same cell orthogonal signals of the target cell. A mobile unit linked to a base station operating in a CDMA IS2000 release C standard based cellular network must periodically determine the defined C/I for nearby base stations. The mobile unit may be required to determine the C/I for nearby base stations while conducting a call with its current base station and thus has limited resources to determine the defined C/I. A need thus exists for a mobile unit based system and method that may be employed to efficiently determine Nt and C/I (as defined by the CDMA IS2000 standard release C) for nearby base stations. The present invention provides such a mobile unit based system and method.